The invention relates to a method for the photolithographic fabrication of a microstructure on a substrate, in particular interconnects of a DRAM (dynamic random access memory) component, with a first exposure with at least one alternating phase mask. The invention further relates to a trimming mask for postexposure during a photolithographic fabrication of a microstructure on a substrate.
Photolithographic methods are often used for fabricating microstructures on a substrate, e.g. a semiconductor material. The methods use a mask with a predetermined pattern for imaging the microstructure onto the substrate. The pattern on the mask thereby comprises light-transmissive (transparent) and light-opaque parts, the light-opaque parts generally being formed by chrome on glass (COG).
In this case, the size and form of the microstructures which can be fabricated by photolithography are limited, in principle, by the light wavelength used and the optical system used in the exposure apparatus.
In order to be able to fabricate microstructures smaller than the light wavelength used during the photolithography, the concept of the alternating phase mask has been developed. In that case, with a mask, a phase shift (0xc2x0/180xc2x0) of the light used for exposure is partly produced in a targeted manner, so that a shadowing is produced in some regions on the semiconductor material in a targeted manner as a result of destructive interference of the light. It is thus possible to form finer microstructures on the substrate, such as e.g. interconnects on a semiconductor substrate, than with masks without an alternating phase shift.
In the case of these phase shift mask assemblies, there is the problem that, in a layout, not all parts of a microstructure can be exposed with a single alternating phase mask, so that particular locations lying between regions with a different phase shift have to be postexposed. Moreover, in a layout design, parts of the microstructure may lie so close together that unambiguous assignment to one of the two phase values is not possible during a postexposure.
The postexposure required is effected with the aid of trimming masks. Such trimming masks correspond to the construction of the conventional COG masks.
What is disadvantageous in this case is that the openings of the trimming masks for postexposure are in turn diffraction-limited, so that it is necessary to comply with a minimum distance between the trimming openings. During the fabrication of very small microstructures, the situation occurs wherein the trimming openings must lie at minimum pitch, that is to say with a distance of twice the minimum structure width (2xc3x97CD critical dimension) of the corresponding photolithography method.
Therein lies a limitation of the postexposure, so that specific fine microstructures cannot be fabricated and the distances between the parts of the microstructure must be increased. This has the result that the microstructures must take up a larger area on the substrate.
It is accordingly an object of the invention to provide a photolithography method for the fabrication of a microstructure on a substrate and to a postexposure trimming mask, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allow very precise postexposure even of very small parts of microstructures, so that the entire microstructure can be arranged in a space-saving manner on the substrate.
With the foregoing and other objects in view there is provided, in accordance with the invention, a photolithography method for fabricating a microstructure on a substrate. The method comprises:
exposing in a first exposure with at least one alternating phase mask;
providing a trimming mask having at least two trimming openings for producing an alternating phase shift; and
exposing in at least one postexposure, following the first exposure, with the trimming mask having the at least two trimming openings.
By virtue of the fact that at least one postexposure is carried out after the first exposure with a trimming mask which has at least two trimming openings for producing an alternating phase shift, it is possible to minimize the distance between the trimming openings. Particularly fine details of a microstructure, such as, for example, interconnects of a DRAM, can thus be fabricated during the postexposure.
It is advantageous if a postexposure with a trimming mask is automatically provided as soon as two parts of the microstructure have or fall below a predeterminable distance.
In accordance with a further advantageous refinement of the method according to the invention, the predeterminable distance is the respective smallest possible value for the distance between microstructures in the case of a predetermined photolithography method.
The substrate is advantageously a semiconductor material, a ceramic or a metal. The method according to the invention can be used during a photolithographic processing of these materials.
Particular advantages are afforded if the microstructure to be produced is a gate structure of a chip, an ASIC (application-specific integrated circuit) or a grid circuit of a DRAM component, since in this case it is necessary to fabricate a multiplicity of particularly closely adjacent microstructures.
With the above and other objects in view there is also provided, in accordance with the invention, a trimming mask for postexposure during a photolithographic fabrication of a microstructure on a substrate. The trimming mask has at least two trimming openings formed therein for producing at least one alternating phase shift.
There is thus also provided, in accordance with the invention a novel trimming mask for a photolithography processing system with an alternating phase mask for exposing the substrate in a first exposure. The trimming mask is provided for postexposure following the first exposure and the trimming mask comprises a trimming mask structure having at least two trimming openings formed therein for producing at least one alternating phase shift in the postexposure.
By virtue of the fact that the trimming mask has at least two trimming openings for producing an alternating phase shift, it is possible to achieve a destructive interference during the exposure for fabrication of small structures.
In accordance with a concomitant feature of the invention, a spacing distance between the at least two trimming openings is less than or equal to a distance defined as a minimum distance between parts of the microstructure relative to a given photolithography process.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for the fabrication of a microstructure and trimming mask for the photolithography, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.